Cooling systems for liquid-cooled internal combustion engines conventionally comprise an engine driven pump for circulating the coolant through the cooling system and a radiator which serves to sink heat from the system to the environment. For engines and engine cooling systems used on a motor vehicle some of this heat may be diverted to the motor vehicle's passenger compartment during cool weather to heat the compartment for the comfort of the occupants. A heat exchanger or “core” through which coolant may be selectively circulated from the engine cooling system provides a way to divert engine heat to the cab for the comfort of the occupants.
Certain motor vehicles, such as large trucks, have occupant compartments (cabs) that include a driver's compartment and a sleeper compartment behind the driver's compartment for use by the driver when not on duty or by a relief driver. It has been expedient in some applications to provide a second core or heat exchanger in the sleeper compartment to better distribute heat through the cab. In the past truck drivers often left the vehicle's main engine running at idle to provide heated coolant for circulation to the passenger and sleeper compartment cores to provide cold weather heating while the vehicle was parked. This had the secondary benefit of keeping the engine warm and avoiding the need for cold restarts, which are notoriously difficult on compression ignition engines. It was also widely recognized that this practice wasted fuel and contributed unnecessarily to air pollution because internal combustion engines running at idle expend too much energy overcoming the engine's parasitic losses for the amount of useful heat produced. As a result the practice of idling a vehicle's primary engine for extended periods to provide heating (or energy for cooling) has been prohibited in many areas.
However, providing climate control on board parked vehicles and pre-heating engines for easier cold weather starts remain valid concerns. Accordingly the art teaches the use of on-board auxiliary coolant heaters which can provide ample heat for these functions without running the engine and incurring the engine's parasitic losses. This is sometimes referred to as “no-idle” heating. One brand of commercially available heaters offers sizes whose heat output range from 5,500 BTU to 120,000 BTU and can run on the gasoline or diesel fuel that is carried by the vehicle. Examples of patents describing similar systems, or related approaches, include U.S. Pat. No. 5,333,678 (describing an auxiliary engine which has sufficient capacity to efficiently run an air conditioner compressor or an electric generator) and U.S. Pat. No. 5,901,780 (a no-idle system). Also of interest is U.S. Patent Application Publication 2007/0063062 for a no-idle system, which is assigned to the assignee of the present application and incorporated herein by reference.
A typical auxiliary coolant heater is reasonably compact and contains components necessary to heat (a burner) and circulate (a pump) engine coolant while the engine is off. The heater may provide heat at different selectable levels, and may be under the control of an associated control unit to maintain a set temperature. When occupant compartment heating is called for, a coolant pump starts circulating coolant through a heat exchanger. A heating device heats the coolant as it circulates so that heated coolant flows out of the heater.